1. Field of the Invention
The present invention relates to novel ceric oxide compositions, and, more especially, to novel ceric oxide particulates, the specific surface of which is stabilized, even at elevated temperatures This invention also relates to the preparation of such particulates and the use thereof, notably in the field of catalysis.
As utilized herein, by the term "specific surface" is intended the B.E.T. specific surface determined by the BRUNAUER-EMMETT-TELLER method, described in J.A.C.S., 60, 309 (1938).
2. Description of the Prior Art:
It is known to this art that ceric oxide may be used both as a catalyst and as a catalyst support. Compare, for example, the publication by Paul Meriaudeau and colleagues relative to the synthesis of methanol from CO +H.sub.2 on platinum catalysts deposited onto ceric oxide; C. R. Acad. Sc. Paris, t. 297 --Serie II-471 (1983).
It is also known to this art that the efficacy of a catalyst generally increases with the area of the contact surface between the catalyst and the reagents. For this, it is necessary to maintain the catalyst in the most highly divided state possible, i.e., the solid particles of which should be as small and as separate as possible. The fundamental role of the support, therefore, is to maintain the particles or crystallites of the catalyst in contact with the reagents in the most highly divided state possible.
Upon extended use of a catalyst support, the specific surface decreases due to the coalescence of the very fine micropores. Over the course of this coalescence, a portion of the catalyst becomes incorporated in the support mass and is prevented from contacting the reagents.
Heretofore, most of the ceric oxides prepared had a specific surface which decreased rapidly at operating temperatures higher than 500 C. Thus, R. Alvero et al., J. Chem. Soc. Dalton Trans., 87, (1984) obtained, from ammonium nitrato cerate, a ceric oxide having, after calcination at 600.degree. C., a specific surface of 29 m.sup.2 /g.
In the Meriaudeau et al publication, supra, for the same type of preparation, a specific surface of 27 m.sup.2 /g was determined.